Invasive Staphylococcus aureus (MRSA/MSSA) Infection Tracking

Staphylococcus aureus is a leading cause of healthcare-associated infections in the United States and an important cause of serious infections in the community. Methicillin-resistant S. aureus (MRSA) is one of the most important antibiotic resistant bacteria in the United States. Data from this project will help inform future policy and prevention strategies to reduce S. aureus disease, including MRSA. Invasive S. aureus is defined as isolated from a normally sterile body site. See the case definition for details.

The invasive S. aureus infection surveillance program is an active population- and laboratory-based surveillance system. Laboratories are specifically and regularly queried by surveillance staff for reports of results among patients in a specifically defined geographic area. This program is conducted through CDC’s Emerging Infections Program (EIP) Healthcare-Associated Infections Community Interface (HAIC). Data from the EIP S. aureus program are used to evaluate the incidence of invasive S. aureus infections in the population, characterize S. aureus strains associated with disease, and monitor trends in disease over time.

The EIP invasive S. aureus infection surveillance program was launched in 2004 as a part of EIP Active Bacterial Core surveillance (ABCs). Between 2004 and 2014, surveillance focused on invasive MRSA infections only in 9 EIP sites. In 2016 it officially became a part of the EIP HAIC activity and incorporated surveillance for both methicillin-resistant and methicillin-sensitive S. aureus. Invasive S. aureus surveillance currently operates in select counties in 7 EIP sites across the United States and has approximately 16 million people living in the surveillance area.

Additional Information

Specifically, the EIP invasive S. aureus surveillance project will:

  • Determine the frequency of invasive S. aureus disease among different patient subpopulations
  • Measure disease trends over time
  • Determine what strains of S. aureus are causing invasive disease

In addition, the project provides infrastructure for further projects, including studies to identify risk factors, determine who would most benefit from vaccines and other interventions in development, and monitor the effectiveness and impact of prevention strategies.

Surveillance Objectives

  1. To monitor changes in incidence of hospital-onset (HO), healthcare-associated community-onset (HACO), and community-associated (CA) invasive infections with Staphylococcus aureus.
  2. To identify populations with invasive S. aureus that would benefit from improved prevention or treatment activities, and assess the impact of established prevention strategies, with a focus on community-onset infections.
  3. To describe the molecular and microbiologic characteristics of strains causing invasive S. aureus infections, with a focus on community-onset S. aureus isolates.


Surveillance Population

Surveillance for invasive S. aureus/MRSA is conducted in seven EIP sites. In some surveillance areas, only invasive MRSA surveillance is conducted. As of July 2015, the total population under surveillance was 15,564,769, according to the U.S. Census Quick Factsexternal icon population estimates accessed June 27, 2016.

Population Under Surveillance (as of January 2016)
State Population (Location)
CA 3,629,776
(3 county San Francisco Bay Area)
CT 3,590,886
(Entire state)
GA 3,701,359
(8 county Atlanta Area)
MD 1,452,977
(Baltimore County and Baltimore City)
MN 1,761,282
(2 metro Twin Cities Counties)
NY 749,600
(1 county Rochester Metro Area)
TN 678,889
(1 county Nashville Metro Area)
Total 15,564,769

Case Definition

To be considered a case, the following conditions must both be met:

  • S. aureus isolated from a normally sterile site, such as blood, cerebrospinal fluid (CSF), pleural fluid, peritoneal fluid, pericardial fluid, bone, joint/synovial fluid, or internal body site (e.g., lymph node, brain)
  • Case patient must be a resident of one of the defined surveillance areas


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